Electrical impedance tomography (EIT) is a known imaging technique, particularly used in medical and other applications for the detection of underlying morphology. Typically, a plurality of electrodes is attached to an object to be imaged. Either input voltages are applied across a subset of ‘input’ electrodes and output electric currents are measured at ‘output’ electrodes, or input electric currents are applied between a subset of ‘input’ electrodes and output voltages are measured at ‘output’ electrodes or between pairs of output electrodes. For example, when a very small alternating electric current is applied between a subset of ‘input’ electrodes, the potential difference between output electrodes or between pairs of ‘output’ electrodes is measured. The current is then applied between a different subset of ‘input’ electrodes and the potential difference between the output electrodes or between pairs of ‘output’ electrodes is measured. An electrical impedance image based on variations in electrical impedance can then be constructed using an appropriate image reconstruction technique.
However, the variations of electrical impedance between regions of different morphology may be too small to be discernible.
One approach to this problem has been to perform EIT over a broad range of frequencies. Different morphologies that have an insignificant impedance difference at one frequency may have a more significant difference at a different frequency. However, even using different frequencies the variations of electrical impedance between portions of different morphology may be too small to be discernible.
It is therefore desirable to be able to better differentiate between different morphologies using EIT.